Fixing for date values.

There is an issue with date fields. `numericValue` is not human readable. Here is an example dump data;

```jacascript
{ row: '1',
  col: '1',
  inputValue: '12/11/2013 11:28:59',
  numericValue: '41619.47846064815',
  '$t': '12/11/2013 11:28:59' }
```

This commit fixes this issue.